Gravity measuring device



BEST AVAILABLE COP.

9 I H. A. WILSON 2,696,713

GRAVITY MEA SURING DEVICE Filed Aug. 17, 1935 6 Sheets-Sheet l BEST AVALABLE COP Aug. 24, 1937. A, w 2,090,713

. GRAVITY MEASURING DEVIC E Filed Aug. 17, 1955 Y 6 Sheets-Sheet 2 BEST AVAILABLE COP Aug. 24, 1937; H. A. WILSON 2,090,713

GRAVITY MEASURING DEVICE Filed Aug. 1'7, 1955 6 Sheets-Sheet 5 BEST AVAILABLE COP 1937. H. A. WILSON GRAVITY MEASURING DEVICE Filed Aug. 17, 1935 6 Sheets-Sheet 4 BEST AVAILABLE COP H. A. WILSON GRAVITY MEASURING DEVICE Aug. 24,, 1937.

Filed Aug. 17, 1935 6 Sheets-Sheet 5 BEST AVAILABLE COP 1937- I H. A. WILSON 2,090,713

GRAVITY MEASURING DEVICE Filed Aug. 17, 1935 6 Sheets-Sheet 6 Patented Aug. 24, 1937 BEST AVAILABLE COP UNITED STATES PATENT OFFICE 2,090,713 GRAVITY MEASURING DEVICE Harold A. Wilson, Houston, Tex., assignor to Standard Oil Development Company, a corporation of Delaware Application August 17, 1935, Serial No. 36,656

24 Claims.

This invention relates to an improved apparatus for comparing the values of gravitational acceleration by plurality of stations. 1

pendulum frequencies are multiplied to radio frequencies,=say to about one million cycles; the approximately million cycle multiplied frequency of the field pendulum is then transmitted to the base station and coincidences are observed with the -similarly multiplied, frequency of the base pendulum. V v H It is an object of the present invention to pro-,

videan-improved-apparatus for the multiplica-Q tionof thefrequency of a pendulum and for the accurate and reliable determination of the diiferences of the accelerations due to gravity bythe observationpf the frequencies of one or more pendulums; i 1 Other objects will be apparent from the specification; and from the accompanying drawings, in which-latter- I v .Fig. l isa diagrammatic representation of a preferredform of apparatus for multiplying the frequency of a pendulum in'which the pendulum is mounted-for rotation about a vertical axis and directs a beam of light in a curved path approximately circularorelliptical. Fig.2 is a diagrammatic representationlof a; preferred form of apparatus showing the pendulum apparatus of. Fig. l disposed at different stations and means for comparing the multiplied frequencies of the pendulums.

Fig. 3 is a perspective view of a modified form of apparatus for comparing the multiplied frequencies of the pendulums. I

Fig. 4 is a perspective view of still another modified form of apparatus for comparing'the multiplied frequencies of the two pendulums.

Fig. 5 is a perspective view of another modified form of apparatus for comparing the multiplied frequencies of the two pendulums.

Fig. 6 is a diagrammatic view of an apparatus for obtaining a multiplication of the frequency of a pendulum arrangement showing in perspective a modified form of pendulum arrangement, operative'to direct a beam of light in a'curved path approximately circular or elliptical.

Fig. '7 is a perspective view of still another modified form of pendulum arrangement operative to direct a beam of light in a curved path, and

8 is a diagrammatic representation of an arrangement for efiecting the rotation of the screen through proper vertical and/or horizontal by the path of light on the screen is large.

Referring particularly to Fig. 1 of the drawings, a pendulum device is illustrated comprising a base I supported by levelling screws 2, 3.and 4. The base carries a pendulum plate 5. A conical pendulum B is supported by the pendulum plate 5 through a point support 9 which rests upon the plate 5'. The top of the conical pendulum 8 is angles when the eccentricity of the ellipse traced fitted with a mirror I I. The conical pendulum I 8 is adaptedto be set in motion so that its center of gravity describ'es a curve in a horizontal plane."

The time required for a complete revolution of the pendulum is determined by the dimensions of the pendulum, the size of the curved path, and the value of the gravitational acceleration at the location where thependulum is being operated.

Means are provided for reflecting a beam of light from. the mirror H on the top of the pendulum 8 in a curved path approximately circular or elliptical. The means comprises asource I2 of 'a' beam of light which" directs the. beam of light iaIon'g the path B through a lens M by meansv offwhi'ch the light beam is. collimatedf The light'beamis reflected from a stationary mirror I5 to the mirror I I, back to the mirror 15 and thence to. a-scanning disc l8. The scanning disc [8 comprises a screen having radial slits [9. .The beam of light follows a curved path onthe screen 18 dueto the linotion of the pendulum 8. Thus, an optical path is designed so that a point of light traces a curved path'on the screen IS in synchronismfwith'therotation of the pendulum 8.

The path, of the beam of light beyond the screen l8 is broken into increments by means of the screen since the light is transmitted only through" the slits" ldfsuccessive pulsations of electric energy, arev created corresponding to the increments, as follows. ,The light transmitted through slits I9 is directed upon a photo-electric cell 2| whereby periodic light impulses are given to the photo-electric cell; Current from the cell 2| is'vcondu'cted throughlines 22 to an amplifier 23 and the amplified current is conducted through lines24ftoafsynchronous motor 25. The syn i chron'ous' motor 25 is operativelyv connected to drive'a disc 26 which indicates the speed of the motor 25." The useoi a plurality of slits in the screen l8 permits of the creation of an equal number of pulsations of electric energyper revo lution of the pendulum and consequently provides'for indicating a multiplication of the frequency of the pendulum. It will be understood that any desired number of impulses per pendulum' revolution can be transmitted through the photo-electric cell to the motor 25. Thus an accurate frequency multiplication of many fold can be'obtained.

Referring particularly to Fig. 2, the pendulum system of Fig. l is shown disposed at both a base station and a field station with a preferred arrangement for comparing the multiplied frequencies of the pendulums. The pendulum systems are used to compare the acceleration of gravity attwo locations. Since the pendulum arrangements at both the base and field stations are identical with that illustrated in Fig. 1, like reference numerals have been applied to like parts in 'these figures. Means are provided for comparing the frequencies of the pulsations of each pendulum system. In the preferred arrangement, the impulses from the photo-electric cell 2| .of the field station are transmitted by conductor or radio to'the base station. For example, assuming the pendulum A inFig. 2'to be disposed at a base station-and the pendulum B to be disposed at a field station,-the conductors 30 leading from the amplifier 23 at the field station conduct the pulsations of electric energyto thesynchronous motor 3'ldisposed' at the base station. Conductors 33 lead from the-amplifier 23 of the base station toajsynchronous motor-34.- The synchronous motors-3| and 34 drive aligned shafts 35 and f'36frespectively. "Ifhe-shafts-35 and 35 carry differentialgears-31 and. 38 respectively. Differential gear 31"is driven by the'fmotor 3 l in one div re ctio nl The difierential'geafiiai s driven by the motor34in the opposite direction." Floating gears 40 and? are operativelyassociated with the difierential gears3'landf33and are seated by a housing -44 which latter 'isf'caused to berotated by the diflerntial 'gear system with a period equal 10 half th difference'in the periods'of rotation of the'isynchronous' motors I'll and 34.-"The period of, rdtationpflthe housing-'44 is therefore, proportional to'the' frequency difference of the pulei ii 1. nenee ii iisv ilms the w" riodsfof the two motors 3 land 34- are compared. particul'alrly tojfig. 3,; an alternative r nf nie tf s' us e or com arin the peo Qiith sai hm motors cr a e ncted withpendulunisystemsdisposed at base 45'and fiel d stations respectively foiicomparing the frequencies of t pulsatignsgenerated at the base 'fgndfield station's; thisfigure reference e al! d ex e sai nch b ons motor c nected*with' thej pendul I h statio d referencenunieral 46 designates a ynch o i s.f i t, i ie'l i' te t e. p dulum"system"'at the"fi eld'stationi The motors 45 and 48 "drivealignedlcoazgial shaftsli48 and 49 re spectively; The adjoining ends of the "shafts 48 and 4'9 and 5 l respectively. If these disc s are marked" any suitable way and e ca sedihitb .re' o e 'i i h same direction,

by the-synchronous motors the marks will come intocoincidenceperifodically with a period which isfthe'di'f'ference betweenthe periddsjofjthe synchronous f. motors. 'Inithe embodiment illustratedfth disc"50is provided withfai narrow radi- J 1 t e 9 i si o i eq'w n a a radlalfslit 54.1 A stationary graduated disc 51 is disposed on'one side of thediscs'jlljand 5i." Dur-' ing rotation of the'jdi'scs so and trimthe same direction a-beam 'o'f lightfr'om' a source'jlnotf shown) on the opposite side of the dis'cs 50 and 5! passes through. the dis'cs50 andSljonly when the" 6 slits 53and 54 coincide. Atjthis timethe'illustrated'stationary disc 51. will'be visible through the slits 5 3fand 5B. The positionofslit coincidence canbe noted by means of an angular scale 59 carried by the stationarydisc 2 nl ternative- 75 ly, the eye of the observer can be disposed oppo-' systemj atfthe' base BEST AVAILABLE COP site the discs 56 and 5! to observe on a scale 59 the point at which the scale is visible upon coincidence of the slits 53 and 54. The time between two successive coincidences of the slits 53 and 54 gives the difference in the periods of the two motors.

Referring to Fig. 4, still another arrangement is shown whereby the frequencies of the pulsations of the pendulum systems at base and field stations-can be compared. In this embodiment, a synchronous motor Si is adapted to be operatively connected with one of the pendulum systerns, for example the one at the base station, and the synchronous motor 52 is adapted to be connected with the other pendulum system. The synchronous motor 6! is provided with a tubular driveshaft 53 which extends through the motor and carries a disc 64 having a radiallydisposed slit 65. The synchronous motor 62 is provided with a drive-shaft 65 which extends through'and protrudes from the tubular shaft 53. The protruding end of the shaft 66 drives a disc 61 which is provided with a radially disposed slit 68. The discs 64 and 61 are driven in rotation in the same direction and the slits 65 and 63 come into coincidence periodically with a period which isthe' difference between the periods of the motors Bil and'62.

tions can be compared. In this embodiment; the

synchronous motor 89'is mounted on a base with its drive shaft l0 vertical.*""I'h "'Syn' chro'- noiis motor 69 is adapted to be operatively 'comnected with one of the pendulum -systezns,'for ex ample the one at the'base station,"- and asynchronous motor ll, adapted to be connected with the other pendulum system, is provided with an armature and drive-shaft 12. The armature and drive-shaft i2 is connected with the drive-shaft 10 by means of a suitable collar 13 whereby the motor II is supported bythe "motor 69'; -The Any suitable way for reading the coincidences can be provided, such as those describedmotor H is provided with magnets-"l l whichare'.

free to turnaro undthe armature shaft I23 The current islet into the mute Tl through-flex ible leads 15;" Alternativ'el 'the cur'rent Tee be let into themotor ll by' m' n'soffcircul'ar'mer- 'cury troughs, not" shown". *I'h'e Ymotor '|I isthus caused to rotatewith a perit'id which is equal the frequency difference of the bf:

pendulum system.

The procedure above ae'cnbed -fdrcsinpenng' periodic motions can be applied to types other than a pendulum having af riearly' or" elliptical motion. If two ordinary 'pnjdulums" are swung with their planes of pulsations atrfight angles to each other, a beam can be made totra'ce a nearly circularpr elliptic path' fwhich-is ia'. composite of the two oscillatory motions."

beam of light falling" on a scanning'disc can be utilized similarly to the beam'of lightfrbm the rotary pendulum as previously described.

- Referring to Fig. 6', a suitablependulumsystemis shownembodyingjhisprinciple and for use at either base or field' 'station., The device comprises a base frame I! 'restinglupon levelingscre'ws 18. Two similar pendulu'ms -ls' and all'are supported by the base Tl 'for' oscillation in the same vertical plane. and 86 are oscillated 180 out'of phase, whereby the horizontal component of forces applied to the base ll by' the pendulums l9 and 80- is can- In operation the pendulums l9 celled out. The pendulums I9 and 88 are mounted in the direction of their swinging and are disposed opposite to each other on the base. In thepreferred embodiment, the base TI is constructed of crossed arms BI and 82. The arm 8I carries plates 83 and 84 upon which rest the knife edges 85 and 86 of the pendulums I9 and 88 respectively. I The pendulums-are suspended in suitable slots 81 in the arm 8|. Mirrors 88 and 89 are attached to the top of pen dulums I9 and 88 respectively.- 7 v Another pair of similar pendulums 98 and 9| is mounted for oscillation in a plane perpendicular to the plane in which the pendulums I9 and 88 are oscillated. The pendulums 98 and 9| are supported by the arm 82. The pendulums 98 and 9| are adapted to be oscillated 180 out of phase in the same vertical plane, whereby the horizontal component of the forces applied to the base I! by these pendulums is cancelled out. The pendulums 98 and BI are provided with knife edges 92 and 93, respectively, which rest on plates 94 and 95 in the conventional manner. Mirrors 96 and 91 are carried by the tops of the pendulums 98 and 9| respectively.

A beam of light is caused to trace a circular path in synchronism with the oscillations of the pendulums, as follows. The beamfof light from a source of light I88 is successively reflected from the mirror 88 to a stationary mirror I8I, to the mirror 91 from which it is reflected and traces a curved path upon a screen I8. The screen I8 and the apparatus for transforming the beam of light into pulsations of electric energy for indicating these pulsations to obtain a multiplication of the frequency of the pendulum device is identical with that described in Figs. 1 and 2, and like reference numerals have been applied to like parts. Similarly, the pendulum system illustrated in Fig. 6 can be set up at both base and fields stations and the frequencies of the pulsations of each system compared, as has been described in connection with Figs. 2, 3, 4 and 5.

Calculation shows that due to difference in I lengths of the optical paths from the two pendulum mirrors in the device of Fig. 6, the point of light may trace an ellipse on the screen I8 instead of a circle. This has no serious disadvantage if the eccentricity is small. However, if it be found that the eccentricity is too large it is easy to rotate the screen I8 through proper vertical and/or horizontal angles so that the point of light will trace a circle on the screen. A preferred form of apparatus for accomplishing this result is illustrated in Fig. 8. In this figure, the scanning disc I8 is shown mounted in a ring I82 fastened by means of bearings I83 and I84 to a similar ring I85 which is fastened by means of bearings I89 and I! to rods I88 and I89. The scanning disc can then be rotated out of the plane of the paper around a vertical axis through bearings I83 and I84 and around a horizontal axis through bearings I88 and I87. It is seen that the arrangement shown in Fig. 8

v is a Cardan suspension.

Referring to Fig. '7, an alternative form is illustrated of a multiple pendulum system for use at either a base or field station for directing a beam of light in a curved path approximately circular or elliptical in synchronism with the oscillations of the pendulums. In this system both of the pendulums of each pair of pendulums swinging 180 out of phase contribute tothe observation data and thereby the accuracy of the results obtained is increased. The same pensss'r AVAlLABLE cow. 3

dulums have been illustrated in the same positions as in Fig. 6, and like reference numerals have been applied to like parts. A beam of light from a source III] is reflected in succession from the mirror 88 to a fixed mirror III, to a fixed mirror I I2, to the mirror 89, to a fixed mirror H8 thence to the mirror 96, to a fixed mirror H thence to a mirror M6, to the mirror 9?, to double-faced mirror IM from which it is directed in a circular path upon the screen I8, as. previously described. As a result of this arrangement tlfe motions of the pendulums I8 and 88 are combined with the motions of the pendulums 98 and 9|. Since the mirror H4 is silvered on both surfaces the beam from the mirror is con-- veniently reflected out of the optical system to the slit screen I8. The beam is caused to pass intermittently through the screen .58 and creates successive pulsations of electric energy, as has been previously described. This pendulum system can be set up at both base and field stations and the frequencies of the pulsations of each system compared as previously described.

Various changes and alternative arrangements may be made within the scope of the appended claims in which it is my intention to claim all novelty inherent in the art as broadly as the prior art permits.

I claim:

1. Apparatus for gravitational prospecting, comprising pendulous means mounted. to swing, a source of a beam of light, means for reflecting the beam of light from the pendulous means whereby the beam describes a circular or elliptical path, means for breaking the path of the:

beam into increments, means for creating successive pulsations of electric energy corresponding to the increments, and means for indicating the pulsations.

2. Apparatus for gravitational prospecting, comprising a pendulum mounted for rotation, a mirror carried by the top of the pendulum, a

' photo-electric cell, a source of a beam of light,

means for reflecting the beam of light from the mirror whereby the beam describes a circular or elliptical path, means for intermittently directing the beam of light upon the cell to actuate the cell to produce pulsations of the electric energy corresponding to a multiple of the frequency of the pendulum, and means for indicating the pulsations.

3. Apparatus for gravitational prospecting, comprising a pendulum mounted for rotation, a mirror carried by the top of the pendulum, a photo-electric cell, a scanning disc having radial slits and disposed between the cell and the mirror, a source of a beam of light, means for de fleeting the beam of light from the mirror whereby the beam describes a circular or elliptical path on a scanning disc around the axis of the slits and intermittently shines through the slits to actuate the cell to produce pulsations of electric energy corresponding to a multiple of the frequency of the pendulum, and means for indicating the pulsations.

4. Apparatus for gravitational prospecting, comprising a pendulum mounted for rotation, a mirrorcarried by the top of the pendulum, a photo-electric cell, a scanning disc having radial slits and disposed between the cell and the mirror, a source of a beam of light, means for deflecting the beam of light from the mirror whereby the beam describes a circular or elliptical path on the scanning disc around the axis of the slits and intermittently shines through the slits to actuate the cell to produce pulsations of electric energy corresponding to a multiple of the frequency of the pendulum, means for amplifying the pulsations, a graduated disc mounted for rotation, and a synchronous motor driven by the amplified pulsations connected to rotate the disc whereby the frequency of the pendulum is indicated by the disc.

5. Apparatus for gravitational prospecting, comprising a pendulum mounted for rotation about a vertical axis, means for creating successive pulsations of electric energy corresponding to equal increments of swing of the pendulum, means for indicating the pulsations comprising a graduated disc mounted for rotation, and a synchronous motor driven by the pulsations connected to rotate the disc whereby the frequency of the pendulum is indicated by the disc.

6. Apparatus for gravitational prospecting, comprising a pendulum system at a base station, a pendulum system at a field station, each system including a pendulum mounted for rotation, a mirror carried by the top of the pendulum, a source of a beam of light, means for deflecting the beam of light from the mirror whereby the beam describes a circular or elliptical path, means for breaking the path of the beam into increments, means for creating successive pulsations of electric energy corresponding to the increments, and means for comparing the frequencies of the pulsations of each system.

'7. Apparatus for gravitational prospecting, comprising a pendulum system at a base station, a pendulum system at a field station, each system including a pendulum mounted for rotation about a vertical axis, a mirror carried by the top of the pendulum, a photo-electric cell, a scanning disc having radial slits and disposed between the cell and the mirror, a source of a beam of light, means for deflecting the beam of light from the mirror whereby the beam describes a circular or elliptical path on the scanning disc around the axis of the slits and intermittently shines through the slits to actuate the cell to produce pulsations of electric energy corresponding to a multiple of the frequency of the pendulum, and means for comparing thefrequencies of the pulsations of each system.

8. Apparatus for gravitational prospecting, comprising a pendulum system at a base station, a pendulum system at a field station, each system including a pendulum mounted for rotation about a vertical axis and means for creating successive pulsations of electric energy corresponding to increments of swing of the pendulum, means for amplifying the pulsations, synchronous motors, one driven from the pulsations from one pendulum system and the other driven by the pulsations from the other pendulum system, a differential gear driven by one motor in one direction, a differential gear driven by the other motor in the opposite direction, and a floating gear operatively associated with the differential gears whereby the speed of rotation of the floating gear is proportional to the frequency difference of the pulsations of each pendulum system.

9. Apparatus for gravitational prospecting, comprising a pendulum system at a base station, a pendulum system at a field station, each system including a pendulum mounted for rotation about a vertical axis, a mirror carried by the top of the pendulum, a photo-electric cell, a source of a beam of light, means for deflecting the beam of light from the mirror whereby the beam describes a circular or elliptical path, means for intermittently directing the beam of light upon the cell to actuate the cell to produce pulsations of electric energy corresponding to a multiple of the frequency of the pendulum, synchronous motors, one driven by the pulsations of one pendulum system and the other driven by the pulsations from the other pendulum system, a differential gear driven by one motor in one direction, a differential gear driven by the other motor in the opposite direction, and a floating gear operatively associated with the differential gears whereby the speed of rotation of the floating gear is proportional to: the frequency difference of the pulsations from each pendulum system.

10. Apparatus for gravitational prospecting, comprising a pendulum system at a base station, a pendulum system at a field station, each system including a pendulum mounted for rotation about a vertical axis and means for creating successive pulsations of electric energy corresponding to increments of swing of the pendulum, synchronous motors, one driven by the pulsations from one system and the other driven by the pulsations from the other system, discs adapted to be driven in rotation in the same direction by the motors and having their axes in alignment, the discs having radially disposed slots, and means for observing the coincidences of the slots whereby variations in the pulsations are observed.

11. Apparatus for gravitational prospecting, comprising pendulums mounted to oscillate about horizontal axes in planes perpendicular to each other, a mirror carried by the. top of each pendulum, a source of a beam of light, means for deflecting the beam of light successively from the mirrors whereby the beam describes a circular or elliptical path, means for breaking the path of the beam into increments, means for creating successive pulsations of electric energy corresponding to the increments, and means for indicating the pulsations,

12. Apparatus for gravitational prospecting, comprising pendulums mounted to oscillate about horizontal axes in planes perpendicular to each other, a mirror carried by the top of each pendulum, a photo-electric cell, a source of a beam of light, means for deflecting the beam of light successively from the mirrors whereby the beam describes a circular or elliptical path, means for intermittently directing the beam of light upon the cell to actuate the cell to produce pulsations of electric energy corresponding to a multiple of the composite frequency of the pendulums, and means for indicating the pulsations.

13. Apparatus for gravitational prospecting, comprising pendulums mounted to oscillate about horizontal axes in planes perpendicular to each other, a mirror carried by the top of each pen dulum, a photo-electric cell, a scanning disc having radial slits and disposed between the cell and the mirrors, a source of a beam of light, means for deflecting the beam of light successively from the mirrors whereby the beam describes a circular or elliptical path on the scanning disc around the axis of the slits and intermittently shines through the slits to actuate the cell to produce pulsations of electric energy corresponding to a mutiple of the composite frequencies of the pendulums, and means for indicating the pulsations.

14. Apparatus for gravitational prospecting, which comprises two pendulum units, each unit comprising two pendulums mounted to oscillate about horizontal axes, the pendulums of each unit oscillating in planes perpendicular to each other, the individual pendulums of each unit being mounted to swing in the same vertical plane and being adapted to swing out of phase, a

plurality of mirrors one carried by the top of' each pendulum, a source of a beam of light, means for deflecting the beam of light successively from a mirror of one unit to and successively from a mirror of the other unit whereby the beam describes a circular or elliptical path, means for breaking the path of the beam into increments, means for creating successive pulsations of electric energy corresponding to the increments, and means for indicating the pulsations.

15. Apparatus for gravitational prospecting, which comprises two pendulum units, each unit comprises two pendulums mounted to swing about horizontal axes, the pendulums of each unit oscillating in planes perpendicular to each other, the individual pendulums of each unit being mounted to swing in the same vertical plane and being adapted to swing 180 out of phase, a plurality of mirrors one carried by the top of each pendulum, a source of a beam of light, means for deflecting the beam of light successively from the mirrors of a pendulum of each unit whereby the beam describes a circular or elliptical path, a photo-electric cell, means for intermittently directing the beam of light upon the cell to actuate the cell to produce pulsations of electric energy corresponding to a multiple of the composite frequencies of the pendulums, and means for indicating the pulsations.

16. Apparatus for gravitational prospecting, which comprises two pendulum units, each unit comprising two pendulums mounted to swing about horizontal axes, the pendulums of each unit oscillating in planes perpendicular to each other, the individual pendulums of. each unit being mounted to swing in the same vertical plane and being adapted to swing 180 out of phase, a plurality of mirrors one carried by the topof each pendulum, a source of a beam of light, means for deflecting the beam of light in succession from the mirrors of one unit and then in succession from the mirrors of the other unit whereby the beam describes a circular or elliptical path, means for breaking the path of the beam into increments, means for creating successive pulsations of electric energy corresponding to the increments, and means for indicating the pulsations.

17. Apparatus for gravitational prospecting, which comprises two pendulum units, each unit comprising two pendulums mounted to swing about horizontal axes, the pendulums of. each unit oscillating in planes perpendicular to each other, the individual pendulums of each unit being mounted to swing in the same vertical plane and being adapted to swing 180 out of phase, a plurality of mirrors one carried by the top of each pendulum, a source of a beam of light, means for deflecting the beam of light in succession from the mirrors of one unit and then in succession from the mirrors of the other unit, whereby the beam describes a circular or elliptical path, a photo-electric cell, a scanning disc having radial slits and disposed in the circular path whereby the beam of light intermittently shines through the slits to actuate the cell to produce pulsations of electric energy corresponding to the composite frequencies of the pendulums, and means for indicating the pulsations.

BEST AVAILABLE CQp\ 5 18. Apparatus for gravitational prospecting, comprising pendulums mounted to oscillate about horizontal axes in planes perpendicular to each other, a mirror carried by the top of each pendulum, a photo-electric cell, a scanning disc having radial slits and disposed between the cell and the mirrors, a source of a beam) of light, means for deflecting the beam of light successively from the mirrors whereby the beam describes an ellipse on the scanning disc around the axis of the slits, means for inclining the disc so that the beam of light traces a circle upon the disc and intermittently shines through the slits to actuate the cell to produce pulsations of electric energy corresponding to a multiple of the composite frequencies of the pendulums, and means for indicating the pulsations.

19. Apparatus for gravitational prospecting, comprising pendulous means mounted to swing, a source of a beam of light, means for reflecting the beam of light from the pendulous means in a circular or elliptical path, means for breaking the path of the beam into increments, and means for indicating the increments.

20. A pendulum comprising a horizontal plate, a point support resting upon the plate, and a hollow inertia member surrounding and depending from the support whereby the center of gravity of the member describes a curve in a horizontal plane.

21. Apparatus for gravitational prospecting, comprising pendulums mounted to oscillate about horizontal axes in planes perpendicular to each other, a source of a beam of light, means for deflecting the beam of light successively from the pendulums whereby the beam describes a circular or elliptical path, means for breaking the path of the beam into increments, and means for indicating the increments.

22. Apparatus for gravitational prospecting, comprising pendulums mounted to oscillate about horizontal axes in planes perpendicular to each other, means for directing and reflecting a beam of light toward said pendulums and thence in a circular or elliptical path, means for breaking the path of the beam into increments, and means for indicating the increments.

23. Apparatus for gravitational prospecting, comprising a pendulum system at a base station, a pendulum system at a field station, each system including a pendulum mounted for rotation about a vertical axis and means for creating successive pulsations of electric energy corresponding to increments of swing of the pendulum, means for amplifying the pulsations'synchronous motors, one driven by the pulsations from one system and the other driven by the pulsations of the other system, discs adapted to be driven in rotation in the same direction by the motors and mounted on a common aXis,the discs having radially disposed slots, and means for observing the coincidences of. the slots whereby variations in the frequencies of each system are observed.

24. Apparatus of the class described, comprising a member mounted for rotation about a vertical axis, a source of a beam of light, means for reflecting the beam of light from the mem ber whereby the beam describes a circular or elliptical path, means for breaking the path of the beam into increments, and means for indicating the increments.

HAROLD A. WILSON. 

